1. Field of the Invention
The present invention relates to cooling towers utilizing fill media. More precisely, the present invention relates to plate type string fill, String-Thick-Plate, being able to be used in open loop cooling towers, which is fabricated with strings, using the unique characteristics of string: flowing down of water on the surface of the vertical or slanted string by gravity, surface tension of string strong enough to hold the water on the surface of string against the strength of draughts in cooling towers, and capability of contacting water and cooling air with barely resisting air flowing.
2. Description of the Related Art
The cooling tower is a key apparatus to prevent industrial hot temperature equipments such as metal melting crucible, extruder, hot sintering electric furnace, etc, as well as a building air conditioning system from breaking down by heat overload. Such cooling towers are categorized into open loop and closed loop cooling towers. The open loop cooling towers related to the present invention use fill medium which is a fill packs fabricated by assembling rectangular thin PVC or Polypropylene film fills by spacing 1.27 to 5.08 cm. Such a film fill pack is an evaporative heat exchanger having a water cooling function by direct contacting water to be cooled and cooling air on the surface of the film fills. The water to be cooled is sprayed on the top of the film fill packs. When the water is sprayed over the top edge of the film fill packs, quite a bit amount of the water breaks into water droplets such as described in http://www.kimre.com/contact_us/AccuPac.pdf, Kimre: ACC-PAC Mist Eliminators. Small droplets of 1-14 μm in diameter flow upward along with cooling airstream, but large droplets of larger than 14 μm in diameter fall free between the film fills. The rest of water flows down over the surface of the film fills by gravity. When the water flowing down on the surface of the film fills is transferred onto the next film fill packs just below the previous film fill packs, some of the water also falls free between the film fills and the rest of the water continuously flows over the surface of the film fills.
The water flowing down on the surface contacts with the cooling air entering the cooling tower from the outside of the cooling tower and traveling over and through the film fills by a fan blower on the top of the cooling tower. Then, after passing through the film fill packs, the air travels out of the cooling tower through the fan blower. While the water and cooling air are passing through the film fill packs, the water transfers some of its preserving heat in it into the cooling air by evaporation and convection process, resulting in cooling the water. And some of the water droplets falling free are combined with the water flowing down on the surface of the film fills to be cooled, but some of them are not. The droplets falling free may not be cooled enough because their contacting time with the cooling air is not long enough due to their fast dropping. There are two ways of contacting the water and cooling air. One of them is a cross current method using a cross current fill packs in which the water flowing down over the surface of the film fills contacts with ambient cooling air traveling in the direction traversing to the descent of the water and the other is a counter current method using a counter current fill packs over which the water flowing down on the film fills contacts with cooling air traveling upwards through the film fill packs.
The water entering the top of the film fills pack in those cooling towers cannot uniformly flow down on the surface of the film fills because the water is directly supplied without passing through a uniform distributor of water. Namely, a large amount of water flows down on some part of the film fills. Owing to such a supplying pattern of water to the cooling towers, the entire surface of the film fills is not perfectly used for cooling the water, which is one of significant disadvantages of the PVC film fills. Another disadvantage is that the air traveling between the plate fills may not affect enough to cool the water on the plate surface because a large portion of the air may be sliding on the surface without interacting with the plate, namely, not contacting with water. To reduce the passing of the air without contacting with the water, the corrugated shape fills and a great number of spacers are employed. Such means may have more chances to resist and block air flowing or create scales and fouling around the corrugated spot and spacers due to creation of the eddy current flow of the water instead of creating contacting surface area. In other words, attachment of spacer between the film fills to maintain their separations and to provide adequate structural support, and production of corrugated shapes to provide adequate strength and rigidity obviously create a large surface area, but it cannot be escaped of those methods to tremendously reduce the cooling effect of water flowing down over the film fills.
The PVC film fills packs used in cooling towers are fabricated assembling a plurality of PVC film fills by gluing attachment tabs on the film fill as described in U.S. Pat. No. 6,715,740 B2. Usually, more than 4,000 bonding tabs to join the PVC film fills together are used in a typical PVC film fills pack of 60.96×30.48×182.88 cm, see more detailed information in http://www.process-vooling.com/copyright/bf9b3bbf7a5b7010VgnVCM′00000f932a8c0, Tower performance, Inc.'s Film Fills-C.E. Shepherd Company, and to make the PVC film fills pack rigid, asbestos-cement or fibrous cement plastic plates are inserted in the PVC film fills pack. Other packing techniques are well summarized in U.S. Pat. No. 6,715,740 B2 and several disadvantages of a PVC film fills pack are extensively described in U.S. Pat. No. 6,715,740 B2 and the most significant disadvantages of the currently using PVC film fills packs are summarized as follows.
1. The asbestos-cement or fibrous cement plates used in the film fills pack absorb significant amount of water when in service to cause in freeze-thaw damage. As results of this, the useful service life of 100 the fills pack tremendously decreases. And also those plates are heavy, high in cost, and hazardous in disposal.2. The thick spacers or attachment tabs between the PVC film fills to maintain their separation and provide adequate structural support also resist the flowing of cooling air between the PVC film fills, which causes to decrease the cooling efficiency of the film fills pack.3. Assembling of adjacent film fills into fills pack is accomplished by using attachment tabs formed on the surface of the film fills. When water is passing down around the spacers of attachment tabs, the flowing rate of water on the underneath of the spacers is relatively so low that scales or fouling are created on those spots. And on the back side of the attachment tabs, concave surfaces are also generated due to production of the attachment tabs so that scales and fouling are created on the 110 concave surfaces. Once the scales and fouling are created, they are growing very fast to resist traveling of the air through the PVC film fills and consequently to reduce the service life of the PVC fill packs.
Such disadvantages of the PVC film fills pack described above are related with the current conventional cooling tower PVC fills pack. The PVC fills packs recently invented such as described in U.S. Pat. No. 6,715,740 B2 for improvement of the current PVC fills packs by compensating their drawbacks also uses the deformable rods or tubes to securely hold the multiple PVC film fills pack in position in the final assembly. They have interior ribs on the surface of the PVC film fills instead of the attachment tabs for maintaining the PVC film fill rigid and strong. At the underneath of the rods or tubes, therefore, the creation of the same scales and fouling cannot be escaped as created at the underneath of attachment tabs in the conventional PVC film fills pack. The interior ribs formed on the surface of the PVC film fills may create an eddy current of water at the corners of the interior ribs to produce scales and fouling on the corners of the ribs. The building up of the scales and fouling reduces flowing rate of the air and finally blocks the air flowing to damage the PVC fills pack. Another disadvantage of the invented technology may be the piling method of the PVC film fills pack in cross stacked fashion. In case of such a piling of the PVC film fills packs, the water flowing down from the previous fills pack may fall free in the air space between the adjacent PVC film fills instead of continuous flowing down on the surface of the PVC film fill, resulting in decreasing the water cooling efficiency of the PVC fills pack.
The evaporative water cooling large string fill pack, one-structure-string-fill-pack, was recently patented by the inventor of the present invention, such as described in Korean Patent NO.s 100393126, 100516391, 100516392, and PCT/KR3004/001825, to replace the PVC film fills pack of the cooling towers. They were invented by eliminating the disadvantages the PVC film fills pack of the current cooling towers. The one-structure-string-fill-packs, heat exchanging media, used in the string evaporative water cooling towers are fabricated with polyester strings and comprises one or more one-structure-string-fill-packs in shape of large rectangular column of 50(W)×25(D)×100(H)cm, fabricated with more than several hundreds of strings. Hence, one rectangular one-structure-string-fill-pack requires a long fabrication time due to threading of strings through the holes on the top and bottom plates separated by 100 cm in the column. The fabrication method is described in Korean Patent No. 100393126. Such a manufacturing feature is a significant disadvantage of the patented string evaporative cooling tower to be brought to marketing. Therefore, it is necessary to have invented a new fabrication technology of a one-structure-string-fill-pack able to tremendously reduce its manufacturing time. To achieve this aim, an innovative String-Thick-Plate (STP) is invented to be easily assembled into a large string fill pack, which is in a rectangular frame whose thickness is in the range of 1 to 5 cm with vertical-string-screens (VSS) on both sides of the STP. The fabrication of the STP is described in the detailed description of the present invention.
The water cooling functions and advantages of the rectangular one-structure-string-fill pack previously invented by the inventor of the present invention are briefly described in this section. When the water to be cooled is sprayed on the top perforated plate of the one-structure-string-fill-pack, the sprayed water spreads over the top perforated plate and is imbibed down through the holes by the surface tension of the strings suspending over and through the holes on the top and bottom plates of the one-structure-string-fill-pack, then flowing down on the surface of the strings. The water flowing down on the surface of the strings becomes circumferential thin film water on the circular surface of the string, which can make a contacting area between water and cooling air maximized and also make the water as thin as possible. Such conditions of the water flowing down on the surface of the strings are significant advantages of the strings to provide high water cooling efficiency of the water. And another significant advantage of the string is that the flowing down of water on the surface of strings do not create any conditions of forming scales and fouling on strings, which means no formation of the scales and fouling in the one-structure-string-fill-pack, resulting in no-reduction of the flowing rate of the cooling air and the serve life of the one-structure-string-fill-pack.
The purpose of the present invention is a fabrication of the innovative STP and STPs pack being free of the disadvantages exhibited in the PVC fill media currently in use and replacing them in the cooling towers, and an inventing of a new technology of fabrication of a large string fills pack requiring a much less fabrication efforts and far lower fabrication cost.